New docker_stack_module with tests (#576)

* First docker stack info approach without tests

Fixes results when no stack availabl

Fixes sanity test

Fixing links

Fixes tabs

Fixes long line

Improving Json Output

Changes arguments

Lint with autopep8

Moves imports

Adds extra line

Adds Tests

Adds pip and fixes return empty

Fixes silly missing else

* Adds Tests and Fixes comments

* Removes tasks option

* Removes arguments

* Changes error message

* Changes Tests

* Add proposals f

* Improve output

* Change test for output change

* Add debug

tests/integration/targets/docker_stack_info/aliases

@@ -0,0 +1,8 @@
+shippable/posix/group1
+skip/aix
+skip/osx
+skip/freebsd
+destructive
+skip/docker  # The tests sometimes make docker daemon unstable; hence,
+             # we skip all docker-based CI runs to avoid disrupting
+             # the whole CI system.